This invention relates generally to impedance transformation amplifiers, and in particular, to techniques for increasing the output voltage or current transformation ratio in an amplifier of this kind.
Impedance transformation amplifiers, as described in U.S. Pat. No. 5,610,553, entitled xe2x80x9cSwitching Amplifier with Impedance Transformation Output Stagexe2x80x9d and incorporated herein by reference, provide output voltage or current exceeding that of the input without the use of a transformer. The maximum voltage or current amplification ratio is limited at low load impedances, however, if high efficiency is to be obtained. Typical voltage ratios with loads under eight ohms are typically limited to 4:1 or less. In some limited voltage applications, the maximum obtainable ratio does not provide adequate power. There exists a need to increase the output amplification ratio in impedance transformation amplifiers, so as to extend their use in higher-power applications.
This invention resides in a method and apparatus for greatly increasing the output voltage or current transformation ratio in an impedance transformation amplifier. Broadly, the method takes advantage of multiple, phase-synchronized impedance transformation stages, each of which preferably contributes an equal portion of the eventual output voltage or current.